[GH-263] Fix wrong class names in SQLAzureFederationsSynchronizer

This issue is created automatically through a Github pull request on behalf of BenMorel:

Url: https://github.com/doctrine/dbal/pull/263

Message:

There is a wrong import in this class:

use Doctrine\DBAL\Sharding\SingleDatabaseSynchronizer;

Should be:

use Doctrine\DBAL\Schema\Synchronizer\SingleDatabaseSynchronizer;

The following import is also missing:

use Doctrine\DBAL\Schema\Synchronizer\SchemaSynchronizer;

This PR fixes them.